The phenotypic expression of a transgene in a plant is determined both by the structure of the gene itself and by its location in the plant genome. At the same time the presence of the transgene at different locations in the genome will influence the overall phenotype of the plant in different ways. The agronomically or industrially successful introduction of a commercially interesting trait in a plant by genetic manipulation can be a lengthy procedure dependent on different factors. The actual transformation and regeneration of genetically transformed plants are only the first in a series of selection steps, which include extensive genetic characterization, breeding, and evaluation in field trials.
Cotton fiber is the single most important textile worldwide. About 80 million acres of cotton are harvested annually across the globe. Cotton is the fifth largest crop in the U.S. in terms of acreage production, with over 15 million acres planted in 2000. Primary weed species for cotton are Ipomoea sp. (morning glory), Amaranthus spp. (pigweed), Cyperus spp. (nutsedge), Xanthium spp. (cocklebur) and Sorghum spp. (johnsongrass). Before the introduction of broad-leaf herbicides that could be used on a growing cotton field, growers used directed, post-emergence applications of nonselective herbicides taking care not to contact the growing crop plants. As this requires a difference in height between the weeds and the crop, this is not always possible. Especially for small cotton, this practice is time-consuming and potentially damaging to the crop.
The bar gene (Thompson et al, 1987, EMBO J. 6:2519-2523; Deblock et al. 1987, EMBO J. 6:2513-2518) is a gene encoding the enzyme phosphinothricin acetyl transferase (PAT), which, when expressed in a plant, confers resistance to the herbicidal compounds phosphinothricin (also called glufosinate) or bialaphos (see also for example U.S. Pat. Nos. 5,646,024 and 5,561,236) and salts and optical isomers thereof. Phosphinothricin controls broadleaf weeds including morning glory and has a wide window of application.
Successful genetic transformation of cotton has been obtained by a number of methods including Agrobacterium infection of cotton explants (Firoozabady et al. 1987, Plant Molecular Biology 10:105-116; Umbeck et al. 1987, Bio/Technology 5:263-266 and in WO 00/71733, U.S. Pat. No. 5,004,863, and U.S. Pat. No. 5,159,135), as well as direct gene transfer by microprojectile bombardment of meristematic cotton tissues (Finer and Mc Mullen, 1990, Plant Cell Reports, 5:586-589; McCabe and Martinell, 1993, Bio/Technology 11:596-598, WO92/15675, EP 0 531 506). Increased transformation efficiency for Agrobacterium transformation has been reported using the methods described by Hansen et al. (1994, Proc. Nat. Acad. Sci. 91:7603-7607) Veluthambi et al. (1989, Journal of Bacteriology 171:3696-3703) and WO 00/71733.
Different methods for regeneration of cotton plants have also been described (WO 89/05344, U.S. Pat. No. 5,244,802, U.S. Pat. No. 5,583,036, WO89/12102, WO93/15622, and WO97/12512).
However, the foregoing documents fail to teach or suggest the present invention.